When, for example, a running vehicle collides with a pedestrian or the like, the pedestrian or the like is thrown onto the bonnet by the impact of the collision. The pedestrian or the like is then subjected to a secondary collision, such as going into the vehicle by breaking the windshield of the vehicle or colliding with a front pillar or the like, and may cause a disaster.
Various pedestrian airbag devices for absorbing and reducing the impact of such a secondary collision have been developed. It is necessary for pedestrian airbags to maintain inflation of the airbags for relatively long period of time, until objects to be protected by the airbags (pedestrians) push into the airbags.
Typically, when a vehicle collides with a pedestrian, a pedestrian airbag device supplies gas generated by an inflator upon the impact into the airbag to inflate and deploy the airbag. In this state, the pedestrian airbag device receives the pedestrian thrown thereon to reduce the impact, and prevents a secondary collision from occurring.
However, if a person thrown into the air collides with an inflated airbag, the person may be seriously injured by the impact. In particular, because a person collided with a car and thrown into the air usually goes into the driver's seat side from the head, if the person pushes into the airbag during inflation, the person may receive serious injury to the head due to the resilience.
An airbag having a gas releasing hole (or a vent hole through which gas is discharged) in a portion thereof for reducing excess pressure to reduce the impact exerted on a pedestrian during pushing into the airbag in an inflated and deployed state is known (refer to Patent Document 1).
However, an airbag which simply has a vent hole allows gas to be released before absorbing impact and fails to maintain inflation of the airbag. Thus, appropriate impact-absorbing characteristics may not be obtained in the initial stage.    [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2001-322518